With more than 10 million people diagnosed with cancer each year and 12% of the deaths worldwide believed to be caused by cancer, there has been an increasing motivation for alternative therapies (who.int/cancer/en). The invasive nature of surgery and adverse effects of conventional chemotherapy and radiotherapy have limited the success of cancer treatment. Frequent administrations of toxic chemotherapy and radiotherapy agents are necessary to minimise their systemic concentration. A more efficient strategy is the delivery of these toxic agents to the tumour sites using targeted delivery systems.
Liposomes and polymeric drug carriers less than 100 nm had been reported to have a tendency to be localised at tumours (Panyam and Labhasetwar, 2003; Allen T M, 2002). This had been attributed to the increased permeability through the tumour vasculature where the cell gap junctions are between 100 to 600 nm. Besides the localisation at tumours and increased surface-to-volume ratio, nanoparticles exhibited other attractive properties unique to its size.
Near infrared (NIR) sensitive nanoshells (Oldenburg et al., 1998) with size and shell thickness dependent properties, are being investigated for applications in hyperthermia (Hirsch et al., Proc Natl Acad Sci USA, 2003), temperature-responsive delivery systems (Sershen and West, 2002) and immunoassays (Hirsch et al.; 2003, Anal Chem). NIR light (λ=650-1000 nm) with its superior propagation in living tissues and signal to background ratio, had been exploited for biomedical imaging (Frangioni J V, 2003), photoablation (Sato et al., 2001) and photodynamic therapy (Dolmans et al., 2003). Haemoglobin and melanin are the major NIR absorbers, while the composition, size and morphology of tissue components also affect the optical penetration. NIR light had been reported to travel through 10 cm of breast tissue and 4 cm of skull tissue using microwatt sources (Weissleder, 2001).
A drug-delivery system, comprising NIR sensitive Au—Au2S nanoparticles with 11-mercaptoundecanoic acid (MUA) adsorbed onto the surface of the nanoparticles and subsequently loaded with cisplatin, was suggested by Ren and Chow, 2003. It was suggested that when NIR light is applied, the cisplatin is released from the nanoparticles to destroy cancerous cells. It has been suggested that such a drug delivery system has the potential to be more efficient, to have reduced toxicity and improved patient compliance and convenience compared to conventional cancer treatments.
Although the system described above has been suggested as a potential drug delivery system, there is a need in the art for a further investigation for a better understanding of the mechanism of interaction between NIR light and NIR sensitive Au—Au2S nanoparticles as well as for the finding of an efficient system for the delivery of drug to a tumour site.